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BACKGROUND Alkaline fermentation of waste activated sludge ( WAS) is feasible to recover carbon for biological nutrients removal. However, it is difficult to abstract the soluble organics from the fermented mixture since sludge dewaterability is deteriorated after fermentation. In this study, a novel system consisting of complete mixing fermentation, water elutriation and settling reactor was developed to produce and abstract short chain fatty acids ( SCFAs) from waste activated sludge through an alkaline fermentation process. RESULTS For the novel system, 57% of sludge solubilization and 327 mg COD g−1 VS of SCFAs production were achieved in the fermentation zone, resulting in a sludge reduction of 54%. In the elutriation zone, nearly 70% of soluble organics was recovered when the water exchange ratio was 33.3%. Moreover, mass balance of the system was calculated and the results showed that C, N, and P element were converted into the liquors phase in the fermentation process with proportions of 54%, 30%, and 16%, respectively. CONCLUSION This work successfully developed a novel process for wasted sludge fermentation and soluble organic carbon separation. Effective results were obtained in the system, indicating it is favorable for pilot and full scale application. © 2017 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Water pollution caused by the highly toxic metal hexavalent chromium (Cr(VI)) creates significant human health and ecological risks. In this study, a novel adsorbent was used to treat Cr(VI)-containing wastewater; the adsorbent was prepared using red mud (RM) generated from the alumina production industry and the rare earth element lanthanum. This study explored adsorption performance, kinetics, and mechanisms. Results showed that the adsorption kinetics of the RM modified by lanthanum (La-RM), followed the pseudo-second-order model, with a rapid adsorption rate. Cr(VI) adsorption was positively associated with the absorbent dose, pH, temperature, and initial Cr(VI) concentration; coexisting anions had little impact. The maximum Cr(VI) adsorption capacity was 17.35 mg/g. Cr(VI) adsorption on La-RM was a mono-layer adsorption pattern, following the Langmuir isotherm model. Thermodynamic parameters showed the adsorption was spontaneous and endothermic. The adsorption of Cr(VI) on La-RM occurred as a result of LaOCl formation on the RM surface, which in turn further reacted with Cr(VI) in the wastewater. This study highlighted a method for converting industrial waste into a valuable material for wastewater treatment. The novel absorbent could be used as a potential adsorbent for treating Cr(VI)-contaminating wastewater, due to its cost-effectiveness and high adsorption capability. [ABSTRACT FROM AUTHOR]

Background The post-denitritation sequencing batch reactor ( SBR) is widely-used and can achieve high levels of nitrogen removal. In this study the effect of influent COD/ TN (total nitrogen) ratio (i.e. C/N ratio) on nitrogen removal performance was investigated. Results The experimental results showed that polyhydroxybutyrate ( PHB) was the internal carbon source for denitritation, so PHB degradation rate following first-order kinetics was the rate-limiting step both for simultaneous nitritation-denitritation ( SND) in the substrate famine period of the oxic stage and endogenous denitritation in the anoxic stage. Higher influent C/N ratio resulted in more PHB fractions in microorganisms, which facilitated a higher efficiency of SND and a faster endogenous denitritation rate ( DNR). Consequently, mean TN removal ratio in oxic stage dropped from 32.81% to 8.61%, and average endogenous DNR in the anoxic stage fell from 1.50 to 0.27 mgN h-1 gVSS-1, when influent C/N ratio changed from 6.82 to 1.89. Furthermore, PHB fraction in the biomass did not drop drastically when influent C/N ratio dropped for a short-term period, which facilitated better resistance to shock loads. Conclusion High influent C/N ration benefits nitrogen removal in this process, and an influent C/N ratio of 4.00 was suitable for advanced nitrogen removal. © 2013 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The effects of acetate and propionate on biological nitrogen and phosphorus removal in a plug-flow A2O process were evaluated in this study. The wastewater quality indexes and operation parameters were the same when different carbon sources were used. However, we observed no obvious effect of carbon source on nitrogen removal. Denitrifying phosphorus removal was found to play an important role in simultaneous nitrogen and phosphorus removal in anoxic reactors because almost the entire carbon source was used for polyhydroxyalkanoate (PHA) synthesis in anaerobic reactors, and there was no external carbon source left for heterotrophic denitrification. Propionate was found to be a more effective and energy-saving carbon source for biological nitrogen and phosphorus removal. In addition, the variations in the metabolic chemicals, such as phosphorus, PHA, glycogen, and oxygen, were lower when propionate was used than when acetate was used. [ABSTRACT FROM AUTHOR]

The control strategy and simulation of external carbon addition were specially studied in an anoxic-oxic (A/O) process with low carbon: nitrogen (C/N) domestic wastewater. The control strategy aimed to adjust the flow rate of external carbon dosage to the anoxic zone, thus the concentration of nitrate plus nitrite (NOx^--N) in the anoxic zone was kept closed to the set point. The relationship was studied between the NOx^--N concentration in the anoxic zone (S_{No}) and the dosage of external carbon, and the results showed that the removal efficiency of the total nitrogen (TN) could not be largely improved by double dosage of carbon source when S_{NO} reached about 2 mg/L. Through keeping S_{NO} at the level of about 2 mg/L, the demand of effluent quality could be met and the carbon dosage could be optimized. Based on the Activated Sludge Model No. 1 (ASM No. 1), a simplified mathematical model of external carbon dosage was developed. Simulation results showed that PI controller and feed-forward PI controller both had good dynamic response and steady precision. And feed-forward PI controller had better control effects due to its consideration of influent disturbances. [ABSTRACT FROM AUTHOR]

In order to improve nitrogen removal in anoxic/oxic (A/O) process effectively for treating domestic wastewaters, the influence factors, DO (dissolved oxygen), nitrate recirculation, sludge recycle, SRT (solids residence time), influent COD/TN and HRT(hydraulic retention time) were studied. Results indicated that it was possible to increase nitrogen removal by using corresponding control strategies, such as, adjusting the DO set point according to effluent ammonia concentration; manipulating nitrate recirculation flow according to nitrate concentration at the end of anoxic zone. Based on the experiments results, a knowledge-based approach for supervision of the nitrogen removal problems was considered, and decision trees for diagnosing nitrification and denitrification problems were built and successfully applied to A/O process. [ABSTRACT FROM AUTHOR]

A novel treating technology for nitrogen removal from soybean wastewater was studied. The process for nitrogen removal was achieved by alternating aeration and mixing, combined with real-time control strategies. Results showed that the COD and total nitrogen removal rates are more than 90% and 92% at COD and total nitrogen loads of 1.0- 1.2 kg COD/(kgMLSS·d) and 0.20-0.27 kg TN/(kgMLSS·d), respectively. In addition, it could improve sludge settling property. SVI value is less than 70 g/ml during the whole cycles. The method not only may be adapted to treat soybean wastewater with high nitrogen, but also may be applied to treat other high nitrogen wastewater. [ABSTRACT FROM AUTHOR]

The Anaerobic-Anoxic/Nitrification (A2N) system is a continuous-flow, two-sludge process in which Poly-p bacteria are capable of taking up phosphate under anoxic conditions using nitrate as an electron acceptor. The process is very efficient because it maximizes the utilization of organic substrate for phosphorus and nitrogen removal. Further, the process solves the competition for organic substrate among Poly-p organisms and denitrifies as well as the problem of overgrowing of slow nitrifiers by fast organotrophs. An experimental lab-scale A2N system fed with domestic sewage was tested over a period of 260 days. The purpose of the experiment was to examine phosphorus removal capacity of a modified A2N two-sludge system. Factors affecting phosphorus and nitrogen removal by the A2N system were investigated. These factors were the influent COD/TN ratio, Sludge Retention Time (SRT), Bypass Sludgy Flow rate (BSF), and Return Sludge Flow rate (RSF). Results indicated that optimum conditions for phosphorus and nitrogen removal were the influent COD/TN ratio around 6.49, the SRT of 14 days, and the BSF and RSF were fixed about 26%–33% of influent flow rate. [ABSTRACT FROM AUTHOR]

A new low cost technology for simultaneous carbon–nitrogen removal from soybean wastewater has been developed in this study. The technology is performed through shortcut nitrification–denitrification. The process operated under real-time control of aeration and mixing time. The shortcut nitrification–denitrification in sequencing batch reactor (SBR) was achieved efficiently and steadily by controlling temperature (28 ± 0.5°C) and using real-time control strategies. This enabled the prevention of nitrite oxidation, leading to lower operational costs. The feasibility of oxidation–reduction potential (ORP) and pH value as control parameter for shortcut nitrification–denitrification process was also investigated. Results showed that the average removal efficiency of ammonium was more than 95%, and nitrosation rate () was reached to 96%. At the same time, the variation of oxidation–reduction potential (ORP) and pH value was well related to organic matter degradation and ammonium oxidation in SBR. So that judgment on the ending of nitrification and denitrification can be based on the inflection point on the varied curve of ORP and pH throughout each SBR processing cycle, and thus reducing aeration and mixing time for saving energy source. The method saves organic energy up to 40% of chemical oxygen demand (COD) in denitrification process, which should reduce the need for an extra external source of organic carbon. Shorter hydraulic retention time should allow the volume of the reactors to diminish, and thus diminish investment costs. Lower oxygen demand of about 25% gives lower exploitation costs. [ABSTRACT FROM AUTHOR]

Quantitative Structure-Activity Relationship (QSAR) between the bio-toxicity of seventy-eight kinds of substituted benzene chemicals to yeast Saccharomyces cerevisiae (lg(1/C[SUBmiz])) and the components of vertex degree autocorrelation vectors (values of A, B, C and D) was studied by using the software of Artificial Neural (Network (ANN). The key factors of the autocorrelation descriptors for the lg (1/C[SUBmiz]) value of yeast Saccharomyces cerevisiae, A [0], A [1], C [3], C [5] and D [3] were selected from twenty-four descriptors, and were explained theoretically in this paper. The QSAR-ANN model has been used to predict the bio-toxicity of twenty-three substituted benzene chemicals. The correlation between C[SUBmiz] and LC[SUB50] was also discussed, and the liner correlation equation between them was established. [ABSTRACT FROM AUTHOR]

In order to study the nitrogen removal via nitrite at normal temperature in anoxic/oxic (A/O) process for treating domestic wastewater, the influence of pH, free ammonia (FA), dissolved oxygen (DO), and hydraulic retention time (HRT) were studied. Results indicated that it was possible to remove nitrogen via nitrite in A/O process, if the temperature was between 18 and 25°C and pH was below 7.5. Even if FA was as low as 0.06 mg NH[SUB3]-N/L, it would inhibit the nitrobacteria. However, FA could not be the sole factor. Whether denitrification went thoroughly or not could affect the nitrification pathway. If denitrification went well, nitrite accumulation could recover in a short while. Nitritification lagged nitratification, so that short HRT would help nitrite accumulation. On the other hand, extended aeration would reduce nitrite accumulation. [ABSTRACT FROM AUTHOR]

Based on the analysis of information flow through the Artificial Neural Network (ANN), a new screening rule of the molecular structure parameter in Quantitative Structure-Activity Relationship (QSAR) was presented by comparing of the values of connection weights and biases of the ANN model. The result showed that model quality and prediction ability of QSAR model, which was constructed by screening structural parameter with ANN, were better than by the method with MLR. The method established the foundation for further study in the mechanism research of the bio-toxicity of organic chemicals. [ABSTRACT FROM AUTHOR]

Control of sludge age and mixed liquid suspended solids concentration in the activated sludge process is critical for ensuring effective wastewater treatment. A nonlinear dynamic model for a step-feed activated sludge process was developed in this study. The system is based on the control of the sludge age and mixed liquor suspended solids in the aerator of last stage by adjusting the sludge recycle and wastage flow rates respectively. The simulation results showed that the sludge age remained nearly constant at a value of 16 d in the variation of the influent characteristics. The mixed liquor suspended solids in the aerator of last stage were also maintained to a desired value of 2500 g/m^3 by adjusting wastage flow rates. [ABSTRACT FROM AUTHOR]